In solid structures, in particular in load-bearing structures of, for example, bridges, buildings, galleries, railways, retaining walls, dams, dykes, slabs and beams of buildings, underground piping and structures of urban subways, and the like, it may be important to monitor, in several points, significant parameters, particularly mechanical stresses (and thus those forces and/or pressures causing the latter) to which the structure is subjected in those locations. In the present description, solid structures are considered such as structures made from construction material, for example cement, concrete, mortar.
Such monitoring, which is carried out either periodically or continuously, is useful both in the initial step and during the life of the structure. To this purpose, electronic monitoring devices are known to be used which are based on electronic sensors capable or providing a good performance while being cost-effective. Usually, these devices are either applied to the surface of the structures to be monitored or within recesses previously provided within the structure and that can be accessed from the outside thereof.
To enhance the performance of the monitoring, in view of evaluating the quality of the structure, the safety, the aging, the reaction to varying atmospheric conditions thereof, and the like, approaches have been also carried out which provide monitoring electronic devices that are “buried” into the material (for example reinforced concrete) of which the structure to be monitored is made. Among them, the device described in the U.S. Pat. No. 6,950,767 is a whole system packaged in one container, which includes several parts that are assembled on a substrate, such as integrated circuits, sensors, antennas, capacitors, batteries, memories, and control units, which are implemented in various “chips” that are connected to each other via metal connections.
As a whole, U.S. Pat. No. 6,950,767 describes an approach of the “System in Package” type (SiP). It should be understood, however, that a SiP, which is first “drowned” in a construction material (e.g. liquid concrete) and intended to remain “buried” within the solid structure, is subjected to environmentally significant conditions, for example due to the very high pressures to which it is subjected, which can even be as high as 600 atmospheres. A number of other wear causes should also be added to the above, which are due for example to water leakage, which can damage the above-mentioned system over time. Therefore, in the above-mentioned field of application, a SiP such as that in U.S. Pat. No. 6,950,767, may be poorly reliable.
Other electronic devices are also known, which are suitable to detect a pressure and consequently the force or mechanical stress that has generated the latter and which are particularly carried out via capacitive pressure sensors. However, these devices cannot be used in the monitoring of the solid structures. In fact, the constructional characteristics of these devices make them vulnerable both to the above-mentioned pressures which are present within the structures and to the effects of corrosion which is caused by water leaking into the structures. Accordingly, these capacitive pressure sensors may also be poorly reliable.